A plant-rich diet may lower dementia risk, even when people start it in their late 50s or 60s, according to a new study.
Older adults who cut many unhealthy foods from their diet over a decade had an 11 per cent lower risk of Alzheimer’s and dementia than adults whose diets did not change, Lim said.
However, people who increasingly ate more unhealthy plant-based options, such as refined grains and foods with added sugars, were about 25 per cent more likely to develop some type of dementia by the end of 10 years, she said.
“The findings suggest that both plant-predominant eating and high diet quality help protect brain function as we age,” said David Katz, a specialist in preventive and lifestyle medicine who was not involved with the study.
Katz founded the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.
The basic definition of a plant-based diet is broad, simply requiring a person to prioritise eating more plant foods than animal products such as meat, milk and eggs.
Under that umbrella, a person could call themselves vegan and still live on sugary, fat-filled, ultra-processed foods known to harm health.
Breakfast, for example, could be an ultra-processed frozen waffle or pancake with imitation maple syrup.
Lunch could include a fast-food veggie burger high in sodium, chips or onion rings high in saturated fat, and a fruit-based fizzy drink packed with sugar.
Dinner could include refined white pasta with high-sugar tomato sauce, followed by ultra-processed biscuits or cake, all plant-based, but not good for brain health.
The report included nearly 93,000 people with an average age of 59 and a diverse mix of ethnicities, African American, Japanese American, Latino, Native Hawaiian and White. All participants were asked about their diets at the start of the study. Ten years later, a smaller group of just over 45,000 people reported on their diet a second time.
The research team scored diets on three tiers of quality. Eating saturated animal fats, dairy, eggs, seafood and meat was the lowest tier.
A tier above that was made up of less healthy plant-based foods such as refined grains, fruit juices, potatoes and added sugars.
Potatoes were placed in the less healthy category because they are high in starch, which quickly turns into glucose in the blood and can trigger blood sugar spikes.
Frying potatoes or adding sour cream and butter also adds extra calories, unhealthy fats and sodium.
Fruit juice can also be less healthy. Drinking apple or orange juice, for example, floods the blood with fructose, a natural sugar found in fruit and some vegetables.
Eating a whole apple or orange does not spike blood sugar in the same way because the fibre in the fruit slows the release of fructose into the blood.
The top tier included the healthiest plant foods, whole grains, fruits, vegetables, vegetable oils, nuts, legumes, and tea and coffee.
The researchers found eating more of these foods was most protective for the brain.
When a subgroup of people who ate the healthiest plant-based foods were compared with each other, those who ate the most foods in this tier lowered their risk of dementia by 7 per cent compared with those who ate the least.
Among the subgroup who ate more unhealthy plant choices, those who ate the largest amount had a 6 per cent greater chance of developing dementia, according to the study.
“We found that adopting a plant-based diet, even starting at an older age, and refraining from low-quality plant-based diets were associated with a lower risk of Alzheimer’s and other dementias,” said lead author Song-Yi Park, associate professor of population sciences at the University of Hawaii Cancer Center.
“Our findings highlight that it is important not only to follow a plant-based diet, but also to ensure that the diet is of high quality.”
Beyond the brain, prior research has shown a healthy plant-based diet was associated with up to a 68 per cent lower risk of diabetes, cardiovascular disease and metabolic risk factors such as high blood pressure.
By contrast, an unhealthier plant-based diet was associated with up to a 63 per cent higher risk.
When it comes to heart health, studies suggest limiting red meat and eating whole grains, legumes and a variety of colourful fruits and vegetables can lower cholesterol and the risk of cardiovascular disease.
The risk of type 2 diabetes was cut by 24 per cent in people who ate the most whole grains, fresh fruits and vegetables, and limited their intake of unhealthy plant and animal foods.
The diet also lowered body mass index and waist circumference.
Eating a healthy plant-based diet has also been linked to longer life and environmental benefits.
A 2023 report by the EAT-Lancet Commission, made up of scientists from 16 countries, found closely following a planet-friendly diet based mostly on fruits, vegetables and whole grains reduced the risk of premature death by nearly one-third, while also cutting greenhouse gas emissions.
“For every major cause of death we looked at, there was a lower risk in people with better adherence to the planetary health diet,” co-author Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health in Boston, said in a previous interview.
“The findings show just how linked human and planetary health are. Eating healthfully boosts environmental sustainability, which in turn is essential for the health and well-being of every person on Earth,” Willett said.